Bacterial pathogens pose a serious threat to public health. Two of the Gram-positive pathogens, Staphylococcus aureus and Enterococcus fecalis/fecium, are primarily nosocomial (hospital-acquired) pathogens; together, they presently account for the majority of nosocomial diseases. Gram-negative bacteria such as Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa, also cause significant diseases in humans. These organisms are aerobic bacteria, i.e., ones that grow in oxygen-containing atmospheres.
Important to health are “anaerobic” bacteria, i.e., those which grow in oxygen-depleted atmospheres, such as are found in intestinal milieu. Gram-positive anaerobes, such as Lactobacilli, Bifidobacteria, and Eubacteria, and Gram-negative anaerobes, such as Bacteroides, represent “good” intestinal organisms important to health, whereas the Gram-positive anaerobes Clostridium difficile and Clostridium perfringens represent pathogenic bacteria. Clostridium difficile (C. diff) has been increasingly associated with disease in human patients, ironically often as a result of treatment with certain antibiotic drugs. The most common disease is referred to as C. diff-associated diarrhea (CDAD).